1. Field of the Invention
The invention relates to an input circuit, and more particularly to an input circuit determining two states or three states at an input pin.
2. Description of the Related Art
Logic input pins of integrated circuits (ICs) generally have two logic states, such as high and low logic states, according input signals. In some applications, logic input pins may have a floating state, representing that the logic input pins receive no signals. Thus, a conventional input circuit is provided to determine two states of an input pin, such as a floating state and a high logic state or a floating state and a low logic state, and further to determine three states thereof, such as a floating state, high and low logic states. When an input pin is at a floating state, the conventional input circuit pulls a level of the input pin high or low through a resistor. For example, when an input pin has a floating state and a high logic state and the input pin is at the floating state, a conventional input circuit pulls a level of the input pin low through a resistor coupled between the input pin and a ground and determines the level of the input pin is low. When the input pin is at the high logic state, the above conventional input circuit determines the level of the input pin is high. However, leakage current is generated on a path formed by the resistor between the input pin and the ground. Thus, it is desired to provide an input circuit that can determine a floating state of an input pin and decrease leakage current when the input pin is at a low or high logic state.